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Cooling Mechanism for Pulsating Heat Load using PCM: A Review
Tapasvi Singh Gehlot1, Dr P M Meena2
1PG
Student Department of Mechanical Engineering, MBM Engineering College, Faculty of Engineering,
Jai Narain Vyas University, Jodhpur, Rajasthan.
2Professor, Department of Mechanical Engineering, MBM Engineering College, Faculty of Engineering,
Jai Narain Vyas University, Jodhpur, Rajasthan.
---------------------------------------------------------------------------***------------------------------------------------------------------------Abstract: The overview of phase change materials (PCMs) and their properties are presented here with the review conducted over
the years. The PCMs discussed here have very high latent heat of fusion, thereby storing large amount of thermal energy over a
narrow temperature range. PCM’s used in high power electronics and direct-energy weapons. High power electronics generate
large pulses heat loads during operations. During heat pulse, the PCM absorb large amount of heat loads. Cooling media is used to
dissipate the heat load with minimization of instantaneous heat load, reduces its physical size and power consumption. Latent
heat storage can be achieved through liquid→solid, solid→liquid, solid→gas and liquid→gas phase changes. However, only
solid→liquid and liquid→solid phase changes are practical for PCMs. Different PCM’s are used as per their utility in different fields
depending on temperature range, thermal conductivity and latent heat etc. which are explained here. PCM’s used in fields such as
mechanical, electrical and commercial area which is explained here.
Keywords: Phase Change Material (PCM); Thermal Energy Storage (TES); Heat exchanger (HEx); Solar water heater
(SWH).
1. Introduction
A Phase Change Material (PCM) is a substance with a high heat of fusion which, melts and solidifies at certain
temperatures, is capable of storing or releasing large amounts of energy. Unlike conventional storage materials, when PCM
reach the temperature at which it changes phase (their melting point) it absorbs large amount of heat without rise in
temperature.
When the ambient temperature in the space around the PCM material drops, the PCM solidifies, releasing its stored
latent heat The thermal energy absorbed by a material when changing its phase at a constant temperature is called ‘latent
heat’. For practical applications, material that exhibit low volume changes is used, for example; solid-to-liquid and some
special solid-to-solid phase change material.
The commonly used phase change materials for technical applications are:
a.
Paraffin’s (Organic)
b.
Salt hydrates (Inorganic)
c.
Organic-organic (Eutectic)
Latent heat storage offers a significant advantage if the application needs temperature cycles closely around the melting
point.
In liquid or solid state the specific heat capacity is lower for most PCM materials compared to water.
PCM therefore absorbs and emits heat while maintaining a nearly constant temperature. Within the human comfort
range of 20° to 30°C, latent thermal storage materials are very effective. They store 5 to 14 times more heat per unit volume
than sensible storage materials such as water, masonry or rock. Latent heat storage is based on the absorption/desorption of
energy when a storage material undergoes a phase change from solid to liquid, liquid to gas, or vice versa. Latent heat storage
is particularly attractive since it provides a high energy storage density and has the capacity to store energy at a constant
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temperature or over a limited range of temperature variation which is the temperature that corresponds to the phase
transition temperature of the material.
For instance, it takes 80 times much as energy to melt a given mass of water (ice) than to raise the same amount of
water by 1oC.One of the potential and effective ways of storing thermal energy in buildings is the integration of brick with
phase change materials (PCMs).
2. Literature Review
TES is a significant technology in systems involving renewable energies as well as other energy resources as it can
make their operation more efficient, particularly by bridging the period between periods when energy is harvested and
periods when it is needed.
That is, TES is helpful for balancing between the supply and demand of energy.
TES systems have the potential for increasing the effective use of thermal energy equipment and for facilitating large-scale fuel
commutating. The selection of a TES system for a particular application depends on many factors, including storage duration,
economics, supply and utilization temperature requirements, storage capacity, heat losses and available space. A complete TES
process involves at least three steps: charging, storing and discharging.
Fig 2.1: The three processes in a general TES system
2.1 TES System classified according to its temperature and thermal storage:
Fig 2.2: Thermal Energy Storage Type
(www.typesofTES.net)
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In sensible heat storage systems (SHSS), thermal energy is stored by raising the temperature of a solid or liquid media.
Such as metal which phase do not change at certain temperature (Only temperature change). In Latent heat storage is one of
the most efficient ways of storing thermal energy. In latent TES systems, energy is stored during the phase change (e.g.
melting, evaporating and crystallization). Unlike the sensible heat storage method, the latent heat storage method provides
much higher storage density, with a smaller temperature difference between storing and releasing heat.
In Thermo-chemical TES systems use an endothermic chemical reaction, where the energy associated with a reversible
reaction is required for the dissociation of the chemicals.
The amount of energy stored is given by the relation:
Q = ∫ m Cp dT = m Cp (Tf – Ti) (Sensible heat storage)
Q = m [∫Cp, s dT + k + ∫ Cp,l dT ] (Latent heat storage)
Q = arm Δhr
(Thermo-chemical heat storage)
Fig 2.3: Graph b/w Temp. & Time
(www.pcmproperties.com)
2.2 PCM materials can be divided in three groups as reported at below:
Fig 2.4: Classification of PCM
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Organic PCMs have a number of characteristics which are non-corrosive, they have a high latent heat per unit weight, they are
recyclable, they melt congruently and they exhibit little or no super cooling i.e. they do not need to be cooled below their
freezing point to initiate crystallization.
Organic materials are divided into two groups:
a.
Paraffin
b.
Non-paraffin
Inorganic materials used as PCM are divided
into salt hydrate, metallic’s and cover a wide temperature range. Compared to organic PCM, inorganic materials usually have
similar melting enthalpies per unit mass, but higher ones per unit volume due to their high density.
a.
Salt Hydrates
b.
Salt
c.
Metallic
A eutectic is a mixture of two or more constituents, which solidify simultaneously out of the liquid at a minimum freezing
point, also called eutectic point. At the eutectic point, the liquid reacts to a solid that is composed of two or more solid phases
with different composition; however, the overall composition is still the same as in the liquid. Therefore, eutectics nearly
always freeze without segregation because they freeze to an intimate mixture crystal. The most common eutectic PCMs are
Triethylolethane + water + urea, Triethylolethane + urea, Mg(NO3)3.6H2O + NH4NO3, Mg(NO3)3.6H2O + MgCl2.6H2O, and
Mg(NO3)2.6H2O + MgBr2.6H2O.12
Table 2.1: PCM Advantage and dis-advantage
Advantages
Disadvantages
Organic
(Paraffins)
Non-corrosive;
Chemically and
thermally stable;
No or little subcooling.
Lower melting
enthalpy;
Lower density;
Low thermal
conductivity;
Flammable.
Inorganic
(Salt Hydrates)
High melting
enthalpy;
High density.
Sub-cooling;
Corrosive
Phase separation;
Phase
segregation, lack
of thermal
Stability;
Cycling stability.
To improve the efficiency of the charging and discharging processes of a PCM-TES system, the most relevant
parameter to be studied is thermal conductivity of the material:
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Fig2.5: Thermal Performance Enhancement Method
Hence, the heat transfer coefficient is dominated by the thermal conductivity of the solid PCM. However,--most PCM
usually provide low thermal conductivity around 0.5W/(m∙K), which results in poor heat transfer between the HTF and the
storage material. Thermal-composites are a term given to combinations of phase change materials (PCMs) and other (usually
solid) structures. In order to increase the thermal-conductivity of PCM, several heat transfer enhancement techniques have
been studied incorporating high thermal conductivity enhancers into PCM and porous heat transfer media, extending heat
transfer surfaces by fins and capsules, using intermediate heat transfer medium or heat pipes and employing multiple PCMs.
Table2.2: Heat exchanger (HEX) can be classified according to performance:
Double pipe HEX
Shell and tube
HEX
Advantages
Suited to high
temperature and
pressure
applications.
Less expensive
compared to
others.
Easy to control
and operatable.
Suited to high
pressure
applications.
Standardization,
Simple maintenance
& servicing.
Flexible and units
can be added and
removed as
required.
Easy in
Construction.
Can be used at low
heat transfer area.
Flat plate type
HEX
Simple
&compact size.
Less
maintenance
cost.
Easy
installation.
Negligible heat
loss.
Capacity can be
increased by
introducing
plates in pairs.
Overall weight
of set is less.
Cheap
Disadvantages
Not compatible
for higher
temperature
and pressure
above 200 and
20 bars.
Leakage corner.
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Maintenance is time
consuming.
Occupy more floor
space compared to
others.
Maintenance cost
is more.
Required large
space.
Initial cost is
high.
Careful
dismantling and
dismantling to
be done.
Application
Used for
refrigeration
process in appliance
like refrigerators,
domestic heating
system and car
radiators.
Used as regular
heat exchanger
for distillation
column, chemical
equipment
stream cooling
and heating
purpose, used
internally in
reboilers and
evaporators.
Used in oil
cooling system
in automobiles,
steam
condensation,
Swimming
water cooling
system,
refrigeration
system.
Fig. 2.6: Double Pipe Heat Exchanger
(www.HEXtypes.com)
Fig. 2.7: Shell and Tube Heat Exchanger
(HEXtypes.com)
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Fig. 2.8: Flat Plate Heat Exchanger
(HEXtypes.com)
2.3 Shell and tube type heat exchanger
a.
The simple design of shell and tube heat exchanger makes it an ideal for a wide variety of application.
b.
To be able to transfer heat well, the tube material should have good thermal conductivity.
c.
The tube material also should be compatible with both the shell and tube side fluids for long periods under the operating
conditions (temperature, pressure, PH etc.) to Minimize deterioration such as corrosion.
d.
All of these requirements call for careful selection of strong, thermally, conductive, corrosion-resistance, high quality tube
material.
2.4 Cooling of Helmet:
A helmet cooling system eliminating the requirement of the power supply uses phase change material (PCM) to absorb all the
heat generated from the head at a relatively constant temperature to provide cooling of the head. Thus, the interior is
maintained at a certain cooled temperature which is close to the melting temperature of the PCM and creates a thermally
comfort environment to the head without requiring electrical power supply. The PCM is enclosed in a pouch and placed
between the head and the helmet. When the head skin temperature is above the melting temperature of the PCM, the PCM
begins to melt as it absorbs the heat from the head.
The basic components of the PCM-cooled helmet are illustrated in Fig. 2.9. The key component of the helmet cooling system is
the PCM pouch, The PCM is enclosed in the pouch, A flexible heat collector made of copper provides a good thermal path for
conducting heat transfer from the wearer head to the PCM pouch, the heat collector is attached to a vinyl cushion which is
filled with a water based solution (gel). The vinyl cushion provides a comfortable interior for the helmet.
The problem of overcooling on the head does not occur as the head skin temperature is maintained at a temperature which is
near to the melting temperature of PCM. The choice of PCM material is important to achieve appropriate cooling on the head.
When the head temperature is above 30 °C (designed temperature to be maintained), the PCM begins to melt to provide a
cooling effect on the head. When the skin temperature is below 30 °C, the PCM pouch provides a warming effect.
Several PCM, such as the organic-based paraffin-based PCM, salt hydrates, certain metallic alloys, and ‘‘dry’’ PCM can be used.
Each has its own strength and weakness for the application. The paraffin PCM is relatively inexpensive and widely available.
Paraffin has higher heat storage capacity per unit volume.
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Fig 2.9: Cooling of Helmet
The cooling unit is able to provide comfort cooling up to 2 h when the PCM is completely melted. The stored heat from
the PCM pouch would then have to be discharged by immersing in water for about 15 min to solidify the PCM before re-use.
2.5 Transportation:
A huge percentage of our food is transported by road with refrigerated vehicles now common place. Controlling the
temperature of food packages during transport is needed with the rise of online shopping. During transport, food requires cold
temperatures to maintain freshness. A major issue is the undesired warming of food when packages are exposed to warm
temperatures on airport tarmacs and temporary unrefrigerated storage during air transportation.
Fig. 2.10: Cooling Of Dairy Product
(www.pcmproducts.com)
PCM technology offers both mechanical-refrigeration-free and back-up cooling options. To solve this problem, phase change
materials (PCMs) can maintain package-temperature by changing their phase from liquid to solid or vice versa, to absorb or
release latent heat. Although this technology is still not fully commercially viable yet, it has good potential.
Table 2.3: Show the Compression transportation facility b/w with and without using PCM (www.pcmproduct.net):
Parameters
Cost of truck and the
insulated container
Cost of the
refrigeration
equipment included
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Without PCM
8.5 Lakhs
With PCM
8.5 Lakhs
Nil
3.75 Lakhs
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PCM and charging unit
for PCM based truck
Cost of the
refrigeration unit for
conventional truck
Total capital cost
Diesel consumption for
the vehicle
Cost of electricity
Total running cost
2.50 Lakhs
Nil
11 Lakhs
4 liters per
hour
Nil
12 Lakhs
2.50 liters
per hour
Rs. 6 per
unit(10 unit
per day)
6.5 Lakh per
annum
10 Lakh per
annum
Investment in capital
cost of PCM based refer
over conventional truck
Saving per annum
using PCM system
1.25 Lakhs ( one time cost)
3.5 Lakh per annum
2.6 TES with PCM for improving energy performance of building:
Some south and oil-exporting countries have also recognized the importance of reducing the energy consumption of buildings
to balance the energy domestic market and exportation.
As stated by Soares et al. some of the most promising passive latent heat TES systems for buildings (for some climates and
certain typologies of buildings) are those related with harnessing solar thermal energy for heating during winter and those
optimized to reduce overheating during summer.
These systems can integrate a vertical stack of rectangular cavities filled with PCMs in their configuration, which is the case of
the exterior PCM-shutter proposed by Soares et al. There are three different ways to use PCMs for heating and cooling of- buildings such as PCMs in building walls, PCMs in building components other than walls i.e. in ceilings and floors, PCMs in
separate heat or cold stores. The first two are passive systems, where the heat or cold stored is automatically released. When
indoor or outdoor temperatures rise or fall beyond the melting point. The third one is active system, where the stored heat or
cold is contained thermally separated from the building by insulation. Therefore, the heat or cold is used only on demand and
not automatically.
In building applications, only PCMs that have a phase transition close to human comfort temperature (20– 28ºC) can be used.
Some Commercial PCMs have been also developed for building application. Material type such that commercial paraffin waxes
to be used as PCMs in passive TES applications for buildings have typically low thermal conductivity (~ 0.2 W m-1 K-1).
Fig 2.11: Cooling Building
(www.pcmapplications.com)
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This TES system was designed to take advantage of solar thermal energy for winter night time indoor heating in Coimbra,
Portugal (Mediterranean climate).
During the night, the system is to be closed to minimize the heat losses through the window and to allow it’s
discharging (releasing the stored energy indoors). Afterwards, the right-side and the left-side shutters can be switched to
solve both the summer and the winter challenges. To improve the heat transfer through the PCM bulk, the small TES unit was
made of aluminum and provided with some horizontal fins connecting the heated/cooled vertical walls, thus forming a vertical
stack of rectangular cavities. The magnitude of the cost savings is more during the summer months whereas the percentage
difference in cost savings is more during winter month. A maximum percentage cost savings of about 30% (October) was observed at the residential utility rate, and 28% (November) was observed at the business utility rate. This suggests that the
currently employed Bio-PCM with melting point of 29 °C works most efficiently in the transition between summer and winter
season during which less intense isolation and ambient temperatures were observed. March was found to have the least cost
savings of around 10% for both the residential and business utility rate. Thermal storage can be part of the building structure,
even for light weight buildings, by the addition of PCMs to gypsum board, plaster, concrete, or other building materials. When
determining the effects of the inlet velocity on melting time, it was found out that it takes approximately half an hour more if
we reduce velocity for 2 m/s. Melting time also increases with modified geometry. If melting temperature is decreased, then
naturally melting time decreases as well, since the temperature difference increases.
Fig 2.12: Charging phase temperature and time graph (www.BCPusingpcm.com).
Fig 2.13: Discharging Phase Temperature and Time Graph (www.BCPusingpcm.com)
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Changing melting temperature range from 24-25°C to 20-24°C, it reduces melting time for one hour. The use of PCM in solar
water heater helps to reduce cooling rate of water, thus it enhance the maximum utilization of solar energy and hence
improves efficiency of system. In this research with use of PCM efficiency of solar water heater increase from 31.25% to
44.63% and also heat storage capacity increase from 3260.4 kJ to 4656.5 kJ.
3. Conclusions
I have presented the information about the types of the PCM and Kind of refrigerant used. Related to my study I learned more
about the theory of heat transfer and its practical application in the real world. There is still a lot to learn and to improve.
Herein the PCM used is ice. Heat Exchanger of shell and tube type is best suitable for this purpose. Phase Change Material has
the wide area of application as an engineering point of view.
Use of PCM can lead to save the energy and proper distribution of the load on the resources such as Demand Side Management
etc. Air Cooling and heating with the help of PCM can help to the air conditioning for human comfort. Cooling of Electronics
equipments with the help of PCM saves the energy to cool the equipments. PCM can be use for the lot of engineering
applications for conservation of energy. The use of PCM in solar water heater helps to reduce cooling rate of water, thus it
enhance the maximum utilization of solar energy and hence improves efficiency of system. In this research with use of PCM
efficiency of solar water heater increase from 31.25% to 44.63% and also heat storage capacity increase from 3260.4 kJ to
4656.5 kJ.
I learned about cooling helmet in which the problem of overcooling on the head does not occur as the head skin temperature is
maintained at a temperature which is near to the melting temperature of PCM. The choice of PCM material is important to
achieve appropriate cooling on the head. When the head temperature is above 30 °C (designed temperature to be maintained),
the PCM begins to melt to provide a cooling effect on the head. When the skin temperature is below 30 °C, the PCM pouch
provides a warming effect. The principal contender of such type of cyclic cooling technology is the Thermal Energy Storage
(TES), in the form of Latent Heat of Fusion, in the Phase Change Materials (PCMs). In this Paper, I learned wide area PCM used
and their properties.
We discussed types of PCM at different areas with different temperature and thermal conductivity.
A literature review on different passive TES systems for buildings and solar water heater are provided.
References
1) Demirbas M.F., Thermal Energy Storage and Phase Change Materials: An Overview, Energy Sources, Part B, 2006.
2) Review of passive PCM latent heat thermal energy storage systems towards mechanical system' energy efficiency" by
Soares et al.
3) Karthikeyan S., Muthu Saravanan S., Prashanth R., Energy conservation through phase change material based thermal
energy storage system-a project report, Anna University Chennai, 2006.
4) Zalba B., Marın J.M., Cabeza L.F., Mehling H., and Review on thermal energy storage with phase change: materials, heat
transfer analysis and applications, Applied Thermal Engineering 23, 2003.
5) Heinz A., Streicher W., Application of phase change materials and classification PCM for thermal energy storage,
Available at: http://talon.stockton.edu. /eyos/ energy_studies /content/docs/FINAL_PAPERS/8B-4.pdf, (accessed
10/05/2012).
6) Gawron K., Schöder J., “Properties of some salt and salt hydrates for latent heat storage”, Energy Research, 1977, Vol.1.
351-363.
7) Wang W. [et al.] Enhanced thermal conductivity and thermal performance of form-stable composite phase change
materials by using β-Aluminum nitride. [Journal] // Applied Energy. - 2008.
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8) “A computational model of a PCM heat exchanger in a vapour compression system with a large pulsed heat load.by
Greg Troszak & Xudong Tang, Proceedings of the ASME 2012 Summer Heat transfer Conference HT 2012.
9) Demand Side Management Through Efficient Thermal, Waqar A. Qureshi, Student Member, IEEE, Nirmal-Kumar C.
Nair, Member, IEEE, Mohammed M. Farid, Non-member.
10) Solar Water Heating System with Phase Change Materials Available from: https:// www.researchgate.net
/publication/265111061_Solar_Water_Heating_System_ with_Phase_Change_Materials.
11) Samira Haghshenaskashani, “HadiPasdarshahri, Simulation of Thermal Storage Phase Change Material in Buildings”,
World Academy of Science Technology. Department of Materials Science & Engineering,
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